Femoral system handle surgical instrument and method of assembling same

ABSTRACT

An orthopaedic surgical instrument assembly includes a system handle configured to clamp a broach and femoral stem trial assembly. The system handle includes a clamp lever and a release lever both pivotally coupled to the system handle, and a leaf spring connecting the clamp lever and the release lever. When the release lever is moved from an unclamped position to a clamped position, the leaf spring is put in tension, and the clamp lever engages a flange of the broach, securing the broach to the system handle. Methods of assembling the system handle are described and claimed.

This application is a divisional of U.S. patent application Ser. No.13/834,862, filed Mar. 15, 2013, which is hereby incorporated byreference.

CROSS-REFERENCE

Cross reference is made to copending U.S. patent application Ser. No.13/834,374 entitled “FEMORAL SURGICAL INSTRUMENT AND METHOD OF USINGSAME,” which is assigned to the same assignee as the present applicationand hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to orthopaedic instruments foruse in the performance of an orthopaedic joint replacement procedure,and more particularly to orthopaedic surgical instruments for use in theperformance of a knee replacement procedure.

BACKGROUND

Joint arthroplasty is a well-known surgical procedure by which adiseased and/or damaged natural joint is replaced by a prosthetic joint.For example, in a total knee arthroplasty surgical procedure, apatient's natural knee joint is partially or totally replaced by aprosthetic knee joint or knee prosthesis. A typical knee prosthesisincludes a tibial tray, a femoral component, and a polymer insert orbearing positioned between the tibial tray and the femoral component.The tibial tray generally includes a plate having a stem extendingdistally therefrom, and the femoral component generally includes a pairof spaced apart condylar elements, which include surfaces thatarticulate with corresponding surfaces of the polymer bearing. The stemof the tibial tray is configured to be implanted in asurgically-prepared medullary canal of the patient's tibia, and thefemoral component is configured to be coupled to a surgically-prepareddistal end of a patient's femur.

From time-to-time, a revision knee surgery may need to be performed on apatient. In such a revision knee surgery, the previously-implanted kneeprosthesis is surgically removed and a replacement knee prosthesis isimplanted. In some revision knee surgeries, all of the components of thepreviously-implanted knee prosthesis, including, for example, the tibialtray, the femoral component, and the polymer bearing, may be surgicallyremoved. In other revision knee surgeries, only part of thepreviously-implanted knee prosthesis may be removed and replaced.

During a revision knee surgery, the orthopaedic surgeon typically uses avariety of different orthopaedic surgical instruments such as, forexample, cutting blocks, surgical reamers, drill guides, prosthetictrials, and other surgical instruments to prepare the patient's bones toreceive the knee prosthesis.

SUMMARY

According to one aspect of the disclosure, an orthopaedic surgicalinstrument includes a handle, a first lever, a second lever, and a leafspring. The handle includes an elongated body extending from a distalend to a proximal end and a guide pin extending from the proximal end.The elongated body has a cavity defined therein. The first lever extendsoutwardly from the cavity to a distal end, the first lever including aproximal end that is pivotally coupled to the elongated body within thecavity. The second lever includes a lever body extending outwardly fromthe cavity to a proximal end, the lever body having a distal end that ispivotally coupled to the elongated body within the cavity, and a catchextending from the proximal end of the lever body. The leaf springconnects the first lever to the second lever such that movement of thefirst lever causes movement of the second lever. The first lever ispivotal between an unclamped position in which the distal end of thefirst lever is spaced a first distance from the elongated body and aclamped position in which distal end of the first lever is spaced asecond distance from the elongated body that is less than the firstdistance. When the first lever is in the unclamped position, the secondlever is in a first position in which the catch is spaced a firstdistance from the guide pin. When the first lever is in the clampedposition, the second lever is in a second position in which the catch isspaced a second distance from the guide pin that is less than the firstdistance. The leaf spring is placed in tension when the first lever isin the clamped position to lock the second lever in the second position.

In some embodiments, the elongated body may include a first side wallhaving a first elongated opening defined therein and a second side wallhaving a second elongated opening defined therein. The first opening andthe second opening may define the cavity in the elongated body.Additionally, in some embodiments the first side wall may include aplurality of first mounting slots defined therein, and the second sidewall may include a plurality of second mounting slots defined therein.The first mounting slots may extend transverse to the first opening, andthe second mounting slots may extend transverse to the second opening.Each second mounting slot may be positioned in a common imaginary planewith one of the first mounting slots.

Additionally, in some embodiments, the first lever may extend outwardlythrough the first opening, and the lever body of the second lever mayextend outwardly through the second opening. In some embodiments, thecavity may include an interior wall facing the second opening. Theinterior wall and the second side wall may define an oblique angle. Thelever body of the second lever may include an arm coupled to the catchand a shoulder coupled between the arm and the distal end. An angledsurface of the shoulder may face the interior wall, and the angledsurface of the shoulder may define an oblique angle with respect to aninterior surface of the arm. The angled surface of the second lever mayengage the interior wall when the second lever is in the clampedposition.

Additionally or alternatively, in some embodiments, the first lever maybe pivotally coupled to the elongated body via a first joint, the firstjoint including a cylindrical pin extending through the elongated bodyand a bore defined in the first lever. The second lever may be pivotallycoupled to the elongated body via a second joint, the second jointincluding a cylindrical pin extending through the elongated body and abore defined in the second lever.

In some embodiments, the first lever may include a first circular slot,and the leaf spring may include a first circular tip that is received inthe first circular slot, the first circular tip having a diameter thatis larger than an opening defined in the first circular slot. The secondlever may include a second circular slot, and the leaf spring mayinclude a second circular tip that is received in the second circularslot, the second circular tip having a diameter that is larger than anopening defined in the second circular slot. In some embodiments, thefirst circular slot may include an insert sized to receive the firstcircular tip of the leaf spring. Additionally, in some embodiments, thefirst lever may include a lever body. The lever body may include a firstend pivotally coupled to the elongated body, and a second end extendingdistally including a grip. The first circular slot may be defined in thelever body between the first end and the second end.

In some embodiments, the elongated body may have a longitudinal axisextending between the proximal end of the elongated body and the distalend of the elongated body, and the first lever may have a longitudinalaxis extending between the proximal end of the lever and the distal endof the lever. The longitudinal axis of the elongated body and thelongitudinal axis of the first lever may define a first angle when thefirst lever is in the unclamped position, and the longitudinal axis ofthe elongated body and the longitudinal axis of the first lever maydefine a second angle when the first lever is in the clamped position.The magnitude of the second angle may be approximately eighty degreesless than the magnitude of the first angle.

According to another aspect, an orthopaedic surgical assembly mayinclude a broach and a handle. The broach may include a tapered outersurface having a plurality of cutting teeth defined therein, a distalsurface having a central aperture defined therein, and a flangepositioned adjacent to the central aperture. The handle may include aguide pin received in the central aperture of the broach, an elongatedbody extending distally from the guide pin, a first lever extendingoutwardly from the elongated body, the first lever including a proximalend that is pivotally coupled to the elongated body, a second leverextending outwardly from the elongated body, the second lever having adistal end that is pivotally coupled to the elongated body, and a leafspring connecting the first lever to the second lever such that movementof the first lever causes movement of the second lever. The second leverincludes a catch engaged with the flange of the broach, and the leafspring applies a clamping force to the second lever. The first lever ismoveable between a clamped position in which the catch is engaged withthe flange of the broach and an unclamped position in which the catch isspaced apart from the flange of the broach.

In some embodiments, the first lever of the handle may be pivotallycoupled to the elongated body via a first joint, the first jointincluding a cylindrical pin extending through the elongated body and abore defined in the first lever. The second lever of the handle may bepivotally coupled to the elongated body via a second joint, the secondjoint including a cylindrical pin extending through the elongated bodyand a bore defined in the second lever.

In some embodiments, the first lever of the handle may include a firstcircular slot, and the leaf spring of the handle may include a firstcircular tip that is received in the first circular slot, the firstcircular tip having a diameter that is larger than an opening defined inthe first circular slot. The second lever of the handle may include asecond circular slot, and the leaf spring may include a second circulartip that is received in the second circular slot, the second circulartip having a diameter that is larger than an opening defined in thesecond circular slot. In some embodiments, the first circular slot mayinclude an insert sized to receive the first circular tip of the leafspring.

In some embodiments, the first lever may include a lever body. The leverbody may include a first end pivotally coupled to the elongated body,and a second end extending distally including a grip. The first circularslot may be defined in the lever body between the first end and thesecond end.

In some embodiments, the elongated body of the handle may have alongitudinal axis extending between the proximal end of the elongatedbody and the distal end of the elongated body, and the first lever ofthe handle may have a longitudinal axis extending between the proximalend of the lever and the distal end of the lever. The longitudinal axisof the elongated body and the longitudinal axis of the first lever maydefine a first angle when the first lever is in the unclamped position,and the longitudinal axis of the elongated body and the longitudinalaxis of the first lever may define a second angle when the first leveris in the clamped position. The magnitude of the second angle may beapproximately eighty degrees less than the magnitude of the first angle.

According to another aspect, a method for assembling an orthopaedicsurgical instrument includes attaching a first lever to a first shell ofa handle, attaching a second lever to the first shell of the handle,inserting a first tip of a leaf spring into a slot of the first lever,inserting a second tip of the leaf spring into a slot of the secondlever, and securing a second shell to the first shell to form thehandle. The first lever extends outwardly from the handle through afirst opening and the second lever extends outwardly from the handlethrough a second opening opposite the first opening.

In some embodiments, attaching the first lever may include attaching thefirst lever after inserting the first tip into the slot of the firstlever and after inserting the second tip into the slot of the secondlever. Attaching the second lever may include attaching the second leverafter inserting the first tip into the slot of the first lever and afterinserting the second tip into the slot of the second lever. Additionallyor alternatively, in some embodiments, inserting the first tip into theslot of the first lever may include inserting the first tip afterattaching the first lever. Inserting the second tip into the slot of thesecond lever may include inserting the second tip after attaching thesecond lever.

In some embodiments, inserting the first tip further may includeinserting a first circular tip of the leaf spring into a circular slotof the first lever, and inserting the second tip further may includeinserting a second circular tip of the leaf spring into a circular slotof the second lever. Additionally, in some embodiments, the method mayfurther include inserting an insert into the circular slot of the firstlever prior to inserting the first circular tip.

In some embodiments, securing the second shell may includes inserting afirst cylindrical pin through a first pair of holes defined in the firstshell and the second shell and a bore defined in the first lever, andinserting a second cylindrical pin through a second pair of holesdefined in the first shell and the second shell and a bore defined inthe second lever.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the following figures,in which:

FIG. 1 is an exploded perspective view of an orthopaedic surgicalinstrument assembly;

FIG. 2 is a cross-sectional elevation view of an orthopaedic instrumenthandle of the instrument assembly of FIG. 1 showing an operating leverin one position;

FIG. 3 is a view similar to FIG. 2 showing the operating lever inanother position;

FIG. 4 is an exploded perspective view of the instrument handle of FIGS.1-3;

FIG. 5 is a perspective view of a depth stop of the instrument assemblyof FIG. 1;

FIG. 6 is an exploded perspective view of the depth stop of FIG. 5;

FIG. 7 is a bottom plan view of the depth stop of FIGS. 5-6;

FIG. 8 is a perspective view of a group of a plurality of spacer platesfor use with the broach stop of FIGS. 5-7;

FIG. 9 is an exploded fragmentary perspective view of the orthopaedicsurgical instrument assembly of FIG. 1;

FIG. 10 is a fragmentary elevation view of the instrument assembly ofFIG. 1; and

FIGS. 11-16 are views of a patient's femur and the orthopaedic surgicalinstrument assembly of FIGS. 1-10 during the performance of anorthopaedic surgical procedure.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific exemplary embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the concepts of the present disclosure tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

Terms representing anatomical references, such as anterior, posterior,medial, lateral, superior, inferior, etcetera, may be used throughoutthe specification in reference to the orthopaedic implants andorthopaedic surgical instruments described herein as well as inreference to the patient's natural anatomy. Such terms havewell-understood meanings in both the study of anatomy and the field oforthopaedics. Use of such anatomical reference terms in the writtendescription and claims is intended to be consistent with theirwell-understood meanings unless noted otherwise.

Referring now to FIG. 1, an orthopaedic surgical instrument assembly 10(hereinafter instrument assembly 10) is shown. As used herein, the terms“orthopaedic surgical instrument” or “orthopaedic surgical instrumentassembly” refer to surgical tools used by a surgeon in performing anorthopaedic surgical procedure. As such, it should be appreciated that,as used herein, the terms “orthopaedic surgical instrument” and“orthopaedic surgical instruments” are distinct from orthopaedicimplants or prostheses that are surgically implanted in the body of thepatient.

The instrument assembly 10 includes an intramedullary surgicalinstrument 12, an orthopaedic surgical instrument handle 14 configuredto be secured to the intramedullary surgical instrument 12, and a depthstop 16 configured to be secured to the instrument handle 14. Asdescribed in greater detail below, the surgeon may use the instrumenthandle 14 and the depth stop 16 to sequentially advance theintramedullary surgical instrument 12 into the medullary canal of thepatient's femur to prepare the femur to receive a femoral prostheticcomponent. The surgeon may also use the depth stop 16 to resect thedistal end of the patient's femur. Although the illustrative instrumentassembly 10 is used to prepare the femur, other embodiments of theinstrument assembly 10 may be used to prepare other bones or joints, forexample the proximal end of the patient's tibia.

The intramedullary surgical instrument 12 includes a femoral stem trial18 coupled to a broach 20. It should be appreciated that in otherembodiments the intramedullary surgical instrument 12 may take otherforms. For example, the stem trial 18 and/or the broach 20 may besubstituted for different sized instruments or different configurations.Additionally, in other embodiments, the intramedullary surgicalinstrument 12 may include a femoral stem trial without a broach, or mayinclude another surgical instrument such as a stem stabilizer.

As shown in FIG. 1, the stem trial 18 of the intramedullary surgicalinstrument 12 has an elongated body 22 that extends from a proximal tip24 to a distal end 26. The distal end 26 has a plurality of externalthreads 28 formed thereon. It should be appreciated that other stemtrials having different configurations may be provided. For example, theouter diameter and/or length of the stem trial may vary to trialprosthetic components of different sizes.

The broach 20 of the intramedullary surgical instrument 12 includes aproximal tip 30 and an outer surface 34 extending from the proximal tip30 to a distal end 36. The tip 30 of the broach 20 includes an aperture32 defined therein that is sized to receive the threaded distal end 26of the femoral stem trial 18. An inner wall defines the aperture 32, andthe inner wall may have a plurality of internal threads formed thereonthat correspond to the external threads 28 of the distal end 26 of thestem trial 18. The aperture 32 and the internal threads thereby maysecure the stem trial 18 to the broach 20.

The outer surface 34 of the broach 20 is tapered, with thecross-sectional area of the broach 20 increasing from the tip 30 to thedistal end 36. A plurality of cutting teeth 38 are formed on the outersurface 34 between the tip 30 and the distal end 36. As described ingreater detail below, the cutting teeth 38 are configured to engage thebone surrounding the medullary canal of the patient's femur when thebroach 20 is inserted therein. It should be appreciated that otherbroaches 20 having different configurations may be provided. Forexample, the outer diameter and/or length of the broach may vary toproduce different sized canals to accommodate prosthetic components ofdifferent sizes.

The broach 20 includes a substantially planar distal surface 40positioned at the distal end 36. A central aperture 42 is defined in thedistal surface 40. The central aperture 42 is sized to receive a guidepin 78 of the instrument handle 14, as described in greater detailbelow. The broach 20 also includes a flange 44 positioned adjacent tothe central aperture 42, which is engaged by an attachment mechanism 50of the instrument handle 14. As described below, a longitudinal axis 46of the broach extends through the tip 30 and the central aperture 42.The axis 46 may be aligned with the anatomical axis of the patient'sfemur when the broach 20 is inserted in the medullary canal, asdescribed in detail below.

As shown in FIG. 1, the instrument handle 14 includes an elongated toolbody 48 and an attachment mechanism 50. The attachment mechanism 50 isconfigured to secure the intramedullary surgical instrument 12 to theinstrument handle 14, as described in detail below. The tool body 48extends from a proximal end 52 to a distal end 54. In the illustrativeembodiment, the tool body 48 is formed from metallic material, such as,for example, stainless steel or cobalt chromium. The tool body 48includes a housing 56 positioned at the proximal end 52 and a grip 58positioned distal of the housing 56. The grip 58 is configured receivethe hand of a surgeon or other user to allow the user to manipulate theinstrument handle 14. Accordingly, the grip 58 may be coated in arubberized or textured material to improve grip stability. In someembodiments, the grip 58 may be formed as a separate unit from thehousing 56 and assembled with the housing 56 to form the tool body 48.

The instrument handle 14 further includes an impaction plate 60 attachedto the grip 58 at the distal end 54 of the tool body 48. The impactionplate 60 is securely attached to the rest of the instrument handle 14,for example by mechanically threading onto the end of the grip 58. Theimpaction plate 60 includes a durable distal surface 62 suitable for usewith a striking tool such as a mallet, sledge, or other impaction tool.The distal surface 62 is large enough to cover the grip 58 in order toshield the hand of the user. In use, the surgeon may impact theimpaction plate 60 to advance the intramedullary surgical instrument 12into the medullary canal of the patient's femur.

The housing 56 of the instrument handle 14 further includes a pair ofside surfaces 64, 66 extending from the proximal end 52 to the grip 58.A pair of openings 68, 70 are defined in the side surfaces 64, 66. Anumber of inner walls 72 extend between the openings 68, 70 through thehousing 56. The inner walls 72 define a cavity 74 inside the housing 56.As described in detail below, the cavity 74 contains components of theattachment mechanism 50. A number of mounting brackets 76 defined in theside surfaces 64, 66. The mounting brackets 76 are configured toseparately engage a mounting bracket 146 of the depth stop 16.

As described above, the instrument handle 12 includes a guide pin 78that is configured to be received by the intramedullary surgicalinstrument 12. The guide pin 78 extends from the proximal end 52 of theinstrument handle 12. The attachment mechanism 50 of the instrumenthandle 14 includes the guide pin 78, a user-operated release lever 80extending distally out of the cavity 74 through the opening 68, and aclamp lever 82 extending outwardly through the opening 70 toward theguide pin 78. When the release lever 80 is moved by the user from anunclamped position to a clamped position, the clamp lever 82 engages theflange 44 of the broach 20 to secure the intramedullary surgicalinstrument 12 to the instrument handle 14 as described below.

Referring now to FIGS. 2 and 3, the attachment mechanism 50 of theinstrument handle 14 further includes a leaf spring 84 that is coupledbetween the release lever 80 and the clamp lever 82. The leaf spring 84includes a circular tip 86 positioned at the proximal end that iscoupled to a complementarily shaped circular slot 88 defined in theclamp lever 82. The leaf spring 84 further includes a circular tip 90positioned at the distal end that is coupled to a complementarily shapedcircular slot 92 defined in the release lever 80. The tips 86, 90 mayrotate within the slots 88, 92, pivotally coupling the leaf spring 84 tothe release lever 80 and the clamp lever 82.

The slot 92 includes an insert 94 configured to facilitate rotation ofthe tip 90 within the slot 92. The insert 94 may be formed from alow-friction polymeric material. The leaf spring 84 has a flexible body96 positioned between the tips 86, 90. The slots 88, 92 include openings98, 100, respectively, through which the flexible body exits the slots88, 92. Each tip 86, 90 has a diameter larger than the respectiveopening 98, 100 thereby mechanically securing the tips 86, 90 within theslots 88, 92. Each tip 86, 90 may be formed from thicker material, beless flexible, and be more durable than the flexible body.

The release lever 80 includes a proximal end 102 that is pivotallycoupled to the tool body 48, a distal end including a grip 104, and alever body 106 coupled between the proximal end 102 and the grip 104.The grip 104 is configured to be gripped by the surgeon or other userwhen moving the release lever 80 between the unclamped position and theclamped position. The slot 92 is positioned in the lever body 106between the proximal end 102 and the grip 104, thereby providingmechanical advantage.

The proximal end 102 of the release lever 80 is pivotally coupled to thetool body 48 via a joint 108. The joint 108 includes circular openings110 extending through the housing 56 and a bore 112 defined in therelease lever 80. The bore 112 encompasses the pivot point of therelease lever 80. A cylindrical cross-pin 114 is positioned in theopenings 110 and the bore 112 such that the release lever 80 is joinedwith the tool body 48. In the illustrative embodiment, the cross-pin 114is press-fit to the opening 110, however, any suitable method ofsecuring the cross-pin 114 may be used.

The release lever 80 includes a longitudinal axis 116 extending betweenthe proximal end 102 and the grip 104. Referring to FIG. 2, thelongitudinal axis 116 is illustrated in the unclamped position 118 andthe clamped position 120. An angle 122 is defined between thelongitudinal axis in the unclamped position 118 and the longitudinalaxis in the clamped position 120. The angle 122 is the throw of therelease lever 80, that is, the angle 122 represents the distance thesurgeon must move the release lever 80 to fully engage the clamp lever82. The angle 122 may have a magnitude of about eighty degrees.

The clamp lever 82 has a roughly triangular, non-linear shape. The clamplever 82 includes an arm 124 extending out of the opening 70 toward theguide pin 78, and a shoulder 126 extending distally from the arm 124toward a distal end 128 positioned within the cavity 74. The arm 124includes a catch 130 configured to engage the flange 44 of the broach 20and thereby secure the broach 20 when the release lever 80 is in theclamped position (see FIG. 3). As described above, the clamp lever 82 ismoveable between an unclamped position (see FIG. 2) and a clampedposition (see FIG. 3). When in the unclamped position, the arm 124 isspaced apart from the guide pin 78. When the clamp lever 82 is movedfrom the unclamped position to the clamped position, the arm 124 movescloser to the guide pin 78 and engages the flange 44. Additionally, whenin the clamped position, the shoulder 126 of the clamp lever 82 mayengage an angled inner wall 132 of the cavity 74. The inner wall 132thus may operate as a stop for the motion of the clamp lever 82. Thedistal end 128 of the clamp lever 82 is pivotally coupled to the toolbody 48. The slot 88 is defined in the distal end 128.

The clamp lever 82 is pivotally coupled to the tool body 48 via a joint134. The joint 134 includes a circular opening 136 extending through thehousing 56 and a bore 138 defined in the clamp lever 82. The bore 138encompasses the pivot point for the clamp lever 82. It should be notedthat the arm 124, the bore 138, and the slot 88 do not lie on a commonline. A cylindrical cross-pin 140 is positioned in the opening 136 andthe bore 138 such that the clamp lever 82 is joined with the tool body48. In the illustrative embodiment, the cross-pin 140 is press-fit tothe opening 136, however, any suitable method of securing the cross-pin140 may be used.

When the release lever 80 is in the extended, or unclamped positionillustrated in FIG. 2, the clamp lever 82 is spaced apart from the guidepin 78. Additionally, the leaf spring 84 has a relaxed, arcuate shape.When the release lever 80 is moved to the clamped position as shown inFIG. 3, the leaf spring 84 has an extended and relatively flattenedshape, causing the leaf spring 84 to be in tension. The leaf spring 84causes the clamp lever 82 to move toward the guide pin 78, securing theintramedullary surgical instrument 12 to the instrument handle 14. Oncein tension, the leaf spring 84 pulls the clamp lever 82 toward thedistal end 54 of the tool body 48 and biases the release lever 80 andthe clamp lever 82 to remain in the clamped position. The intramedullarysurgical instrument 12 may be released by moving the release lever 80from the clamped to the unclamped position.

Referring now to FIG. 4, the instrument handle 14 may be assembled fromcomponent parts by inserting the tip 86 of the leaf spring 84 into theslot 88 of the clamp lever 82. The insert 94 may be inserted into theslot 92 of the release lever 80. The tip 90 of the leaf spring 84 may beinserted into the slot 92 of the release lever 80. The assembled clamplever 82, leaf spring 84, and release lever 80 may be inserted into thecavity 74 of the housing 56 through one of the openings 68, 70. Theclamp lever 82 may be pivotally secured to the tool body 48 by insertingthe cross-pin 140 through the bore 138 and the openings 136. The releaselever 80 may also be pivotally secured to the tool body 48 by insertingthe cross-pin 114 through the bore 112 and the openings 110.

Referring now to FIGS. 5-7, the depth stop 16 includes a base plate 142that defines a substantially planar proximal surface 144 that may beused by the surgeon to seat the intramedullary surgical instrument 12 atthe proper depth in the patient's medullary canal. The depth stop 16also includes a mounting bracket 146 coupled to the base plate 142. Themounting bracket 146 is configured to engage one of the mountingbrackets 76 of the instrument handle 14, as mentioned above. The depthstop 16 additionally includes a locking mechanism 148 that is configuredto secure the instrument handle 14 to the depth stop 16, as described ingreater detail below.

The base plate 142 of the depth stop 16 includes a pair of arms 150 thatcooperate to define the proximal surface 144 of the depth stop 16. Achannel 152 extending through the proximal surface 144 is definedbetween the arms 150 and is sized to receive the housing 56 of theinstrument handle 14. In the illustrative embodiment, the proximalsurface 144 may be used by the surgeon as a non-captured distal cuttingguide to resect the distal end of the femur, as described in more detailbelow.

The base plate 142 includes a distal surface 154 positioned opposite theproximal surface 144. The distal surface 154 and the proximal surface144 are separated by a wall 156 having a maximum thickness 158. In someembodiments, the thickness 158 may be equivalent to the thickness of aprosthetic femoral component to be installed. In some embodiments, thethickness 158 may be approximately nine millimeters.

Each of the arms 150 may include a cylindrical passageway 160 extendingparallel to the proximal surface 144. The passageways 160 are configuredto secure additional surgical instruments to the depth stop 16 such as amodular cutting guide or a measurement gauge, as described below. Thepassageways 160 may be partially exposed through the proximal surface144 as illustrated (see FIG. 5), or in some embodiments may be fullycontained within the arms 150.

The mounting bracket 146 of the depth stop 16 is secured to the baseplate 142 opposite the proximal surface 144. The mounting bracket 146includes a pair of flanges 162 configured to engage each of the mountingbrackets 76 of the instrument handle 14. A channel 164 is definedbetween the flanges 162 that is more narrow than the channel 152 definedby the arms 150. Thus, the flanges 162 stabilize the depth stop 16 byengaging the corresponding one of the mounting brackets 76. A corner ofeach flange 162 includes a chamfer 166 to allow the depth stop 16 toslide onto the instrument handle 14 more readily. Although illustratedas including a pair of flanges 162, in some embodiments the mountingbracket 146 may include a single flange, lug, or other projectionconfigured to be received by each of the mounting brackets 76 of theinstrument handle 14.

The channels 152, 164 further define an axis 168 that intersects theproximal surface 144 (see FIG. 7). The axis 168 and the proximal surface144 define an oblique angle 170; that is, the axis 168 is notperpendicular to the proximal surface 144. In use, the oblique angle 170accounts for the angle between the anatomical axis of the patient'sfemur and the joint line between the femoral component and the polymerbearing of the prosthetic knee joint. The magnitude of the angle 170matches the prosthetic component; in other words, the angle 170corresponds to the angle between the distal surface of the femoralcomponent and the anatomical axis. In some embodiments, the angle 170may have a magnitude of approximately 85 degrees. Further, the angle 170extends outward laterally for both right-handed and left-handed knees.Therefore, a specialized depth stop 16 may be used for either theright-hand knee or the left-hand knee.

The mounting bracket 146 further includes a notch 172 configured toallow any markings on the instrument handle 14 associated with theengaged mounting bracket 76 to be visible when the depth stop 16 isattached to the instrument handle 14.

Referring now to FIG. 6, the depth stop 16 further includes the lockingmechanism 148, which is configured to secure the depth stop 16 to theinstrument handle 14. The locking mechanism 148 includes a latch plate174 configured to slide within the mounting bracket 146, a pair of pins180, 182 configured to secure the latch plate 174 to the mountingbracket 146, and a biasing element 184. The latch plate 174 includes acatch 176 positioned on one end that is configured to engage theinstrument handle 14. On the other end, the latch plate 174 includes auser-operated button 178 that is operable to selectively engage ordisengage the catch 176. In the illustrative embodiment, the button 178includes a contoured outer surface that is configured to receive afingertip of a surgeon or other user. The latch plate 174 furtherincludes an elongated opening 186 defined near the catch 176, and anaperture 188 defined near the button 178.

The pin 180 is positioned within the elongated opening 186 of the latchplate 174 and a bore 190 defined in the mounting bracket 146. Thus, theelongated opening 186 defines the range of travel for the latch plate174. The pin 182 is positioned within the aperture 188 and a bore 192defined in the mounting bracket 146. The biasing element 184, in theillustrative example a spring, is positioned between the latch plate 174and the pin 182. The biasing element 184 presses against the latch plate174 and biases the catch 176 in the engaged position shown in FIG. 7.When the button 178 is pressed in a direction indicated by the arrow194, the latch plate 174 moves to a disengaged position. The latch plate174 further includes a cam surface 196 positioned on the catch 176.

Referring now to FIG. 8, the instrument assembly 10 may be used with anumber of spacer plates 198 that each may be attached to the depth stop16. Each of the spacer plates 198 includes a substantially planarproximal surface 200 opposite a distal surface 202. The proximal surface200 and the distal surface 202 are separated by a wall 204 having athickness 206.

Each of the spacer plates 198 further includes a pair of pins 208 thatare used to secure the plate to the depth stop 16. The depth stop 16includes a pair of mounting holes 210 defined in a substantially planarwall 212 connecting the proximal surface 144 and the mounting bracket146. The mounting holes 210 extend from the wall 212 through the arms150 parallel to the proximal surface 144. The pins 208 of each of thespacer plates 198 may slide into the mounting holes 210, securing thespacer plate 198 to the depth stop 16. When the spacer plate 198 issecured to the depth stop 16, the distal surface 202 engages theproximal surface 144 of the depth stop 16. In some embodiments, one ormore additional or different attachment devices may be secured to thedepth stop 16 using the mounting holes 210, for example a mountingbracket for a captured cutting block or mounting pins of a capturedcutting block. In some embodiments, a captured cutting block may beattached to similar mounting holes of the spacer plate 198 (not shown).

When the spacer plate 198 is secured to the depth stop 16, the surgeonmay use the proximal surface 200 of the spacer plate 198 as anon-captured distal cutting guide, as described in greater detail below.Each of the spacer plates 198 may have a different thickness 206,allowing the surgeon to select an appropriate cutting depth. Forexample, spacer plates 198 may be embodied with thicknesses 206 of 4millimeters, 8 millimeters, 12 millimeters, and 16 millimeters. Thus,when a spacer plate 198 is attached to the depth stop 16, the positionof the proximal surface 144 is effectively moved closer to the distalend of the broach 20 by the thickness 206 of the spacer plate 198.

Referring now to FIG. 9, the depth stop 16 may be attached to theinstrument handle 14 by aligning the channels 152, 164 of the depth stop16 with the mounting brackets 76 of the instrument handle 14. Eachmounting bracket 76 may be embodied as a pair of slots 214 defined inthe side surfaces 64, 66 extending transversely across the openings 68,70. Each pair of slots 214 may be positioned on a common imaginary plane216. The flanges 162 of the depth stop 16 are aligned with one of thepairs of slots 214. It should be noted that in some embodiments, ratherthan as the pairs of slots 214, each of the mounting brackets 76 may beembodied as a single recess formed in the exterior of the tool body 48that is configured to receive the mounting bracket 146 of the depth stop16. The depth stop 16 may then be brought into contact with theinstrument handle 14.

As the depth stop 16 is brought into contact with the instrument handle14, the flanges 162 engage the selected one of the pairs of slots 214.As the depth stop 16 further engages the instrument handle 14, theflanges 162 slide along the selected pair of slots 214, and the camsurface 196 of the locking mechanism 148 is advanced into contact withthe housing 56 of the instrument handle 14. The engagement of the camsurface 196 and the housing 56 causes the latch plate 174 to move in thedirection indicated by the arrow 194 to disengage the catch 176. As theflanges 162 slide further along the selected pair of slots 214, the camsurface 196 disengages, allowing the spring 184 to urge the catch 176 toreturn to the engaged position, thereby securing the depth stop 16 tothe instrument handle 14. The flanges 162 slide along the selected pairof slots 214 until the housing 56 contacts the wall 156 of the depthstop 16 positioned at the end of the channel 164.

The intramedullary surgical instrument 12 may be attached to theinstrument handle 14 by aligning the central aperture 42 of the broach20 with the guide pin 78 of the instrument handle 14, and the flange 44of the broach 20 with the catch 130 of the instrument handle 14. Theinstrument handle 14 is advanced with the release lever 80 in theunlocked position, moving the guide pin 78 into the central aperture 42until the proximal end 52 of the tool body 48 engages the distal surface40 of the broach 20. The grip 58 and the release lever 80 of theinstrument handle 14 are squeezed together to move the release lever 80to the clamped position, and the catch 130 engages the flange 44,thereby securing the broach 20 to the instrument handle 14. When therelease lever 80 is in the clamped position, the leaf spring 84 providesclamping force to secure the intramedullary surgical instrument 12 tothe instrument handle 14.

Referring now to FIG. 10, as described above, the angle 170 is definedby the proximal surface 144 and the axis 168 that is defined by thechannels 152, 164 of the depth stop 16. The angle 170 is also defined bybroach axis 46 and the proximal surface 144 when the instrument assembly10 is assembled, because when properly assembled the broach axis 46 andthe axis 168 coincide. Also as described above, the angle 170 may have amagnitude of about eighty-five degrees.

Further, when the instrument assembly 10 is assembled, a distance 218 isdefined between the distal surface 40 of the broach 20 and the proximalsurface 144 of the depth stop 16. Because the angle 170 causes suchdistance 218 to vary over the extent of the proximal surface 144, thedistance 218 may be defined as the shortest distance between a point 220on the distal surface 40 of the broach 20 that intersects the broachaxis 46 and the proximal surface 144. The distal surface 154 of thedepth stop 16 is positioned further away from the distal surface 40 ofthe broach 20 by the thickness 158, which is constant over the extent ofthe proximal surface 144.

Each of the mounting brackets 76 is associated with a predetermineddistance 218 between the proximal surface 144 and the distal surface 40of the broach 20. Thus, the surgeon may select the mounting bracket 76for attachment based on the desired distance 218. A set of markings 222on the housing 56 may assist the surgeon in selecting the mountingbracket 76. The markings 222 are visible through the notch 172 of thedepth stop 16. It should be noted that in other embodiments, rather thanincluding several mounting brackets 76, the instrument handle 14 mayinclude a single mounting bracket 76. In that example, the instrumentassembly 10 includes a number of depth stops 16, each having a differentthickness 158. Accordingly, in that example the distance 218 depends onthe selected depth stop 16.

The instrument assembly 10 may be utilized during the performance of anorthopaedic surgical procedure similar to that shown in FIGS. 11-16. Asshown in FIGS. 11-15, the surgeon may initially prepare the medullarycanal. The surgeon may then assemble the instrument assembly 10 andinsert the intramedullary surgical instrument 12 into the medullarycanal. As shown in FIG. 16, the surgeon may resect the distal surface ofthe femur as necessary. As shown in FIG. 16, the surgeon may attachadditional orthopaedic instruments to the broach 20 to further preparethe distal surface of the femur.

The surgeon initially prepares the medullary canal 302 of the patient'sfemur 304. To do so, the surgeon may insert an initial surgical reamerinto the medullary canal 302. In some embodiments, the threaded distalend 26 of the stem trial 18 may be secured to the reamer prior toinsertion in the medullary canal 302. The surgeon may use the reamer todrill and/or ream the medullary canal 302 to the depth and/or diameterrequired to receive the broach 20 and/or the stem trial 18. Multipledrills or reamers may be used to increase the size of the opening of themedullary canal formed on the distal end of the patient's femur. Whenthe reaming operation is complete, the medullary canal 302 is configuredas shown in FIG. 11 and is ready to receive the intramedullary surgicalinstrument 12.

After preparing the medullary canal 302, the surgeon assembles theinstrument assembly 10 by attaching the depth stop 16 and theintramedullary surgical instrument 12 to the instrument handle 14 asdescribed above. As described above, the surgeon may select a depth stop16 specialized for either the right-hand knee or the left-hand knee.Before assembly, the surgeon may plan the final depth of theintramedullary surgical instrument 12 in relation to a distal surface306 of the patient's femur 304. The depth depends on the size ofprosthetic femoral component to be installed. The depth may also dependon the condition of the distal surface 306 of the patient's femur 304.The surgeon may make this determination pre-operatively orintraoperatively, depending on the condition of the patient's femur 304.For example, if large amounts of bone are deteriorated or missing, thesurgeon may select a shallower final depth, that is, the surgeon maydistalize the position of the broach 20.

Based on the planned final depth of the intramedullary surgicalinstrument 12, the surgeon selects a mounting bracket 76 located in anappropriate position on the instrument handle 14 and attaches the depthstop 16 to that selected mounting bracket 76. The surgeon may referencethe markings 222 when selecting the mounting bracket 76. To distalizethe broach 20 beyond the limits of the mounting brackets 76, the surgeonmay attach one of the spacer plates 198 having an appropriate thickness206 to the depth stop 16 (see FIG. 14). Thus, by attaching the depthstop 16 to the selected mounting bracket 76 and optionally attaching anappropriate spacer plate 198, the surgeon has set the distance 218between the distal end 36 of the broach 20 and the proximal surface 144of the depth stop 16. As described above, in a different embodiment, toset the distance 218 the surgeon may choose a depth stop 16 from anumber of depth stops 16 having different thicknesses 158, and attachthe selected depth stop 16 to the mounting bracket 76.

After attaching the depth stop 16, the surgeon may assemble theintramedullary surgical instrument 12 by threading the distal end 26 ofthe stem trial 18 onto the tip 30 of the broach 20. The surgeon may alsosecure the intramedullary surgical instrument 12 to the instrumenthandle 14 by positioning the central aperture 42 of the broach 20 overthe guide pin 78 of the instrument handle 14, engaging the distalsurface 40 of the broach 20 with the instrument handle 14, and squeezingthe release lever 80 into the clamped position.

The surgeon may align the surgical assembly 10 with the medullary canal302 of the patient's femur 304 as shown in FIG. 11. To do so, thesurgeon aligns the broach axis 46 with an anatomical axis 308 of thefemur 304 that extends through a distal opening 310 of the medullarycanal 302. The surgeon may then drive the intramedullary surgicalinstrument 12 into the femur 304 along the anatomical axis 308 bystriking the impaction plate 60 of the instrument handle 14 with mallet,sledge, or other impaction tool. As the intramedullary surgicalinstrument 12 is driven into the bone, the cutting teeth 38 of thebroach 20 engage the patient's femur 304 to shape the medullary canal302 to receive the prosthetic femoral component or a femoral trialcomponent.

As the intramedullary surgical instrument 12 is advanced into the bone,as shown in FIG. 12, the surgeon may evaluate the position of theintramedullary surgical instrument 12 with respect to the distal surface306 of the femur 304. The distal surface 154 of the depth stop 16defines an imaginary joint line 312. The joint line 312 represents theplanned contact line between the prosthetic femoral component and theprosthetic tibial bearing of the knee prosthesis. Thus, the surgeon mayrefer to the joint line 312 when assessing whether the intramedullarysurgical instrument 12 is positioned properly in the medullary canal302. The surgeon may use the distal surface 154 of the base plate 142 asa visual reference for the joint line 312. Additionally, the surgeon mayuse the curved shape of each of the arms 150 as a visual reference thatechoes the shape of the condyles of the prosthetic femoral component. Atthis stage of the procedure, the surgeon may determine to distalize thebroach 20 and attach one of the spacer plates 198 to the depth stop 16as described above.

The surgeon may advance the intramedullary surgical instrument 12 intothe medullary canal 302 along the anatomical axis 308 of the femur 304until the proximal surface 144 of the depth stop 16 (or the proximalsurface 200 of a spacer plate 198) engages the distal surface 306 of thefemur 304 as shown in FIG. 13. If both condyles 314 of the femur 304 areequally distal and free of defects, the proximal surface 144 may contactboth condyles 314. If one of the condyles 314 extends further distallythan the other condyle 314, the proximal surface 144 may contact themost distal condyle 314, as shown in FIG. 13. When the proximal surface144 is engaged with the distal surface 306, the distance 218 between theproximal surface 144 and the broach 20 determines the depth of thebroach 20 in the medullary canal 302.

After or during broaching, the surgeon may determine whether to resectthe distal surface 306 of the femur 304. The surgeon may determine toresect the distal surface 306 to remove irregularities and provide aclean bone surface for fixation of the prosthetic femoral component. Toperform the resection, as shown in FIG. 13, the surgeon may insert a sawblade 316 of a surgical saw between the proximal surface 144 and thedistal surface 306 of the femur 304. The surgeon may engage the femur304 to remove the desired amount of bone, using the proximal surface 144as a reference. Thus, the proximal surface 144 may act as a non-captureddistal cutting guide. As shown in FIG. 14, in some embodiments, a spacerplate 198 may be attached to the depth stop 16. In such embodiments, theproximal surface 200 of the attached spacer plate 198 may used as anon-captured distal cutting guide, similarly to the proximal surface144. As described above, in some embodiments a captured cutting blockmay be attached to the broach stop 16 or the spacer plate 198 to performthe resection. After resecting the femur 304, the surgeon may continueto advance the intramedullary surgical instrument 12 along theanatomical axis 308 until the proximal surface 144 (or the proximalsurface 200 in some embodiments) engages the freshly cut distal surface306 of the femur 304, as described above.

Referring now to FIG. 15, in some embodiments, the surgeon may attach ameasurement gauge 402 to the depth stop 16. A measurement gauge suitablefor use with the depth stop 16 is shown and described in U.S. patentapplication Ser. No. 13/780,836 entitled “FEMORAL ORTHOPAEDIC SURGICALINSTRUMENT INCLUDING A MEASUREMENT DEVICE AND METHOD OF USE OF SAME,”which is incorporated herein by reference. The measurement gauge 402includes an arm 404 and a mounting shaft 406 extending from the arm 404.As described above, the mounting shaft 406 of the measurement gauge 402may slide into the passageway 160 defined in one of the arms 150 of thedepth stop 16, thereby securing the measurement gauge 402 to the depthstop 16. The arm 404 of the measurement gauge 402 includes a number ofreference markings 408. When secured to the depth stop 16, each of thereference markings indicates a predetermined distance from the jointline 312. The markings 408 include a zero indicator 410 that is alignedwith the joint line 312. While advancing the broach 20 into themedullary canal 302, the surgeon may reference the markings 408 todetermine the position of the joint line 312 in relation to features ofthe femur 304, for example, the distal surface 306 or the condyles 314.

After the intramedullary surgical instrument 12 is in position and anyresection is complete, the surgeon may further prepare the medullarycanal 302 and the femur 304 to receive the prosthetic implant. Thesurgeon may release the instrument handle 14 from the broach 20 bypulling on the release lever 80, moving the release lever 80 to theunlocked position. After removing the instrument handle 14, theintramedullary surgical instrument 12 remains seated within themedullary canal 302. As shown in FIG. 16, the surgeon may secure anintramedullary adapter 412 to the intramedullary surgical instrument 12.The intramedullary adapter 412 is a surgical tool configured to besecured to the intramedullary surgical instrument 12 and including anend sized and shaped to be positioned in a medullary canal of apatient's femur during the orthopaedic surgical procedure. To secure theintramedullary adapter 412 to the intramedullary surgical instrument 12,the surgeon may engage a captured bolt 414 of the intramedullary adapter412 with the central aperture 42 of the broach 20 and tighten thecaptured bolt 414. The central aperture 42 may include a threaded innersurface configured to receive the captured bolt 414.

The surgeon may further attach a modular cutting block 416 to theintramedullary adapter 412. The modular cutting block 416 includes abase plate 418 and a pair of curved arms 420 that extend posteriorlyfrom the base plate 418. Each of the curved arms 420 may correspond to acondylar surface of the prosthetic femoral component. The modularcutting block 416 further includes a number of cutting guides 422 thatthe surgeon may use to prepare the distal surface 306 of the patient'sfemur 304. The surgeon may attach additional sub-modules to the modularcutting block 416 to perform additional cuts to prepare the patient'sfemur 304 (not illustrated).

After installing the modular cutting block 416, the surgeon may use agap assessment tool 424 to assess the position of the femur 304 inrelation to the patient's tibia 318. The gap assessment tool 424 may beused to assess the joint space between a patient's femur 304 and tibia318 including, for example, the flexion and extension gaps of thepatient, and the size the prosthetic implants. After completingpreparation of the femur 304, the surgeon may loosen the captured bolt414 and remove the intramedullary adapter 412 and the modular cuttingblock 416 from the patient's femur 304.

Last, after completing preparation of the patient's femur 304, thesurgeon may reattach the instrument handle 14 to the broach 20 andremove the intramedullary surgical instrument 12 from the medullarycanal 302. After removal, the surgeon may proceed with implantation ofprosthetic components.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such an illustration and descriptionis to be considered as exemplary and not restrictive in character, itbeing understood that only illustrative embodiments have been shown anddescribed and that all changes and modifications that come within thespirit of the disclosure are desired to be protected.

There are a plurality of advantages of the present disclosure arisingfrom the various features of the method, apparatus, and system describedherein. It will be noted that alternative embodiments of the method,apparatus, and system of the present disclosure may not include all ofthe features described yet still benefit from at least some of theadvantages of such features. Those of ordinary skill in the art mayreadily devise their own implementations of the method, apparatus, andsystem that incorporate one or more of the features of the presentinvention and fall within the spirit and scope of the present disclosureas defined by the appended claims.

1. An orthopaedic surgical assembly comprising: a broach including (i) atapered outer surface having a plurality of cutting teeth definedtherein, (ii) a distal surface having a central aperture definedtherein, and (iii) a flange positioned adjacent to the central aperture,and a handle including (i) a guide pin received in the central apertureof the broach, (ii) an elongated body extending distally from the guidepin, (iii) a first lever extending outwardly from the elongated body,the first lever including a proximal end that is pivotally coupled tothe elongated body, (iv) a second lever extending outwardly from theelongated body, the second lever having a distal end that is pivotallycoupled to the elongated body, and (v) a leaf spring connecting thefirst lever to the second lever such that movement of the first levercauses movement of the second lever, wherein (i) the second leverincludes a catch engaged with the flange of the broach, and (ii) theleaf spring applies a clamping force to the second lever, wherein thefirst lever is moveable between (i) a clamped position in which thecatch is engaged with the flange of the broach and (ii) an unclampedposition in which the catch is spaced apart from the flange of thebroach.
 2. The surgical assembly of claim 1, wherein: the first lever ofthe handle is pivotally coupled to the elongated body via a first joint,the first joint including a cylindrical pin extending through theelongated body and a bore defined in the first lever, and the secondlever of the handle is pivotally coupled to the elongated body via asecond joint, the second joint including a cylindrical pin extendingthrough the elongated body and a bore defined in the second lever. 3.The surgical assembly of claim 1, wherein: the first lever of the handleincludes a first circular slot, the leaf spring of the handle includes afirst circular tip that is received in the first circular slot, thefirst circular tip having a diameter that is larger than an openingdefined in the first circular slot, the second lever of the handleincludes a second circular slot, and the leaf spring includes a secondcircular tip that is received in the second circular slot, the secondcircular tip having a diameter that is larger than an opening defined inthe second circular slot.
 4. The surgical assembly of claim 3, whereinthe first circular slot includes an insert sized to receive the firstcircular tip of the leaf spring.
 5. The surgical assembly of claim 3,wherein the first lever includes a lever body having: a first endpivotally coupled to the elongated body, and a second end extendingdistally including a grip, wherein the first circular slot is defined inthe lever body between the first end and the second end.
 6. The surgicalassembly of claim 1, wherein: the elongated body of the handle has alongitudinal axis extending between the proximal end of the elongatedbody and the distal end of the elongated body, the first lever of thehandle has a longitudinal axis extending between the proximal end of thelever and the distal end of the lever, the longitudinal axis of theelongated body and the longitudinal axis of the first lever define afirst angle when the first lever is in the unclamped position, thelongitudinal axis of the elongated body and the longitudinal axis of thefirst lever define a second angle when the first lever is in the clampedposition, and the magnitude of the second angle is approximately eightydegrees less than the magnitude of the first angle.
 7. A method forassembling an orthopaedic surgical instrument comprising: attaching afirst lever to a first shell of a handle, attaching a second lever tothe first shell of the handle, inserting a first tip of a leaf springinto a slot of the first lever, inserting a second tip of the leafspring into a slot of the second lever, and securing a second shell tothe first shell to form the handle, wherein (i) the first lever extendsoutwardly from the handle through a first opening and (ii) the secondlever extends outwardly from the handle through a second openingopposite the first opening.
 8. The method of claim 7, wherein: attachingthe first lever includes attaching the first lever after inserting thefirst tip into the slot of the first lever and after inserting thesecond tip into the slot of the second lever, and attaching the secondlever includes attaching the second lever after inserting the first tipinto the slot of the first lever and after inserting the second tip intothe slot of the second lever.
 9. The method of claim 7, wherein:inserting the first tip into the slot of the first lever includesinserting the first tip after attaching the first lever, and insertingthe second tip into the slot of the second lever includes inserting thesecond tip after attaching the second lever.
 10. The method of claim 7,wherein: inserting the first tip further includes inserting a firstcircular tip of the leaf spring into a circular slot of the first lever,and inserting the second tip further includes inserting a secondcircular tip of the leaf spring into a circular slot of the secondlever.
 11. The method of claim 10, further including inserting an insertinto the circular slot of the first lever prior to inserting the firstcircular tip.
 12. The method of claim 7, wherein securing the secondshell includes: inserting a first cylindrical pin through a first pairof holes defined in the first shell and the second shell and a boredefined in the first lever, and inserting a second cylindrical pinthrough a second pair of holes defined in the first shell and the secondshell and a bore defined in the second lever.